Volvo penta 4.3 GL

[Lawnpro979]

being a new boat to me. the former owner stated that he just had it serviced. and I have NO reason to doubt this. BUT I forgot to ask. " he retired and moved outta state" BUT please correct me.....

It's my understanding if you had regular oil. then you cant go synthetic.... and If I can go synthetic. what preps should I do ? Drainage all the oil and such......
and is Mobil 1 ok?

Thanks a Million.... I'm Very confused....